Photographic diffusion transfer reversal processes



March 22, 1955 5 LAND 2,704,721

PHOTOGRAPHIC DIFFUSION TRANSFER REVERSAL PROCESSES Filed April 22, 1954 Suppor'l lOq IO Phoi'osensiHve Silver lOb Halide Layer I4 Liquid Composilion |2b 'l'ubilizing Ageni 2 I [20 uppor+ FIG. I

Coni'qinzr 2O Sheei Suppori FIG. 2

INVENTOR ATTORNEYS United States Patent PHOTOGRAPHIC DIFFUSION TRANSFER REVERSAL PROCESSES Edwin H. Land, Cambridge, Mass., assignor to Polaroid Corporation, Cambridge, Mass., a corporation of Delaware Application April 22, 1954, Serial No. 424,883 18 Claims. (Cl. 95-88) This invention relates to photographic processes and more particularly to silver halide diffusion transfer reversal processes wherein a latent image in a silver halide emulsion is developed and wherein soluble silver complex obtained by reaction with the undeveloped silver halide of said emulsion is caused to diffuse to a suitable print-receiving material and to form therein a positive print of the said latent image.

This application is a continuation-in-part of my 00- pending application Serial No. 176,963, filed August 1, 1950 for Photographic Transfer Processes and Compositions for the Practice of Said Processes, now abandoned, and the latter application is in turn a continuation-in-part of the application which issued as Patent No. 2,662,822 on December 15, 1953 for Photographic Transfer Processes and Compositions for the Practice of Said Processes.

Silver halide transfer processes for producing positive prints in a single step and suitable for use in hand-held cameras for taking snapshots have been described in my Patent No. 2,543,181, issued February 27, 1951 for Photographic Product Comprising a Rupturable Container Carrying a Photographic Processing Liquid, and Patent No. 2,603,565, issued July 15, 1952 for Photographic Film-Forming lmage Transfer Composition, and also in the aforesaid Patent No. 2,662,822.

One important requirement of these processes, if they are to be successfully adapted for giving positive prints almost immediately after exposure, is that they operate over a wide range of temperatures, and it is accordingly one object of the present invention to provide improvements in said processes and in the liquid compositions for performing said processes, whereby it becomes possible to obtain pictures of consistently good quality at elevated temperatures up to and in excess of 110 F. Ordinarily, there is a tendency for the print quality to deteriorate if the processing is performed at the higher range of temperatures and, according to the present invention, suitable materials are incorporated, preferably in the processing composition, which materially minimize this tendency so that prints of good quality can be had at the higher temperatures.

More specifically, an object of the present invention is to provide a novel diffusion transfer reversal process for giving positive prints of good quality over a wide range of temperatures by including in the processing composition not only the reagents required for the development of the silver halide emulsion and for the formation of the positive print but at least one further novel addition agent for maintaining said reagents effective at elevated temperatures.

This substance is a compound having two fused rings in its structure, one of said rings being a benzene ring and the other being a S-membered heterocyclic ring which shares two carbon atoms with the benzene ring. The other three atoms of said 5-membered ring include two nitrogen atoms attached to the shared carbons of said ring and a third atom from the class consisting of nitrogen and carbon. Three of the four unshared carbons of said benzene ring have hydrogen attached there to and the fourth has a substituent from the class consisting of hydrogen, chlorine, nitro and methyl groups. Thus, the compound has the following structural formula:

2,704,721 Patented Mar. 22, 1955 wherein X is attached to one of the unshared carbon atoms of the benzene ring and is one of H, N02, C1 and CH3 and wherein Y is one of CH and N. Illustrative of compounds of this type are chlorobenzotriazole, 6- nitrobenzimidazole, benzotriazole, S-nitrobenzotriazole, and S-methylbenzimidazole. These addition agents are preferably contained in the processing composition in relatively low concentrations of the order of one part or less in 500 parts by weight of the processing composition.

Other objects of the present invention will in part be obvious and will in part appear hereinafter.

The invention accordingly comprises the process involving the several steps and the relation and order of one or more of such steps with respect to each of the others which are exemplified in the following detailed disclosure, and the scope of the application of which will be indicated in the claims.

For a fuller understanding of the nature and objects of the invention, reference should be had to the following detailed description taken in connection with the accompanying drawing wherein:

Figure 1 is a diagrammatic, enlarged, sectional view illustrating the association of elements during one stage of the performance of the novel transfer process of the present invention, the thicknesses of the various materials being exaggerated; and

Fig. 2 is a diagrammatic, perspective view, with parts broken away, of a novel product comprising a container which carries the processing composition of the invention and a support upon which said composition is spreadable from said container.

The present invention is primarily concerned with the processing of an exposed silver halide emulsion to give directly, and without further exposure, a positive print of the subject matter of a latent image in said emulsion, and particularly with processes wherein the prints are obtained by the development of the emulsion and by the transfer of a portion at least of the silver of the unexposed regions of said emulsion to a suitable silver-receiving layer, the silver, upon precipitation in said receiving layer, producing a visible image.

In one preferred form of the process of the present invention the development of the latent image and the transfer and precipitation of the silver from the undeveloped regions of the silver halide emulsion occur almost concurrently. A liquid composition is so applied to the surface of a photosensitive silver halide element as to be absorbed in part into the emulsion of said element, and this single liquid application develops the penetrated portion of the emulsion and causes the formation of a soluble silver complex with the remaining undeveloped silver halide in the penetrated portion. The liquid composition is best applied in a thin, uniform, relatively viscous layer, for example by being spread on the emulsion.

The process is characterized by the inclusion in the thin liquid layer of a substance which is capable of maintaining the process efiective at elevated temperatures so that at temperatures of the order of F. there is still obtained by the process a positive transfer print of good pictorial quality. As hereinbefore pointed out, one class of substances particularly suitable as the addition agents for effecting this result are compounds having the following structural formula:

wherein X is attached to one of the unshared carbon atoms of the benzene ring and is one of H, N02, Cl and CH3 and wherein Y is one of CH and N.

The processing agent which contains this novel reagent for maintaining print quality at elevated temperatures preferably also has dispersed therein, as by dissolution, a solid material which suitably thickens the composition. Because of its increased viscosity, the material spreads more uniformly over the photosensitive element and it is additionally evident that, upon application of a layer of such a composition to a photosensitive element, the liquid solvent of the composition will permeate into and be absorbed by said element and will in part evaporate, thereby increasing the concentration of the thickening agent at the surface of the element and eventually forming a practically solid film of said thickening agent adjacent to said surface. This film, by also containing therein a suspension of a suitable silver precipitating agent, may serve to receive the silver that is precipitated from the soluble silver complex and may have the transfer print formed therein. The thickening agent is preferably a film-forming colloid or a plastic capable of producing a self-supporting solid film when the liquid is entirely removed therefrom and such a film, upon solidification, may be peeled from the negative with the silver image therein.

The viscous liquid composition is best applied to the surface of the photosensitive element by being spread between the photosensitive element and another sheet material, such as paper. The advantages of using the second sheet are manifold. It provides a base for the film of processing agent when the latter serves as the silver-receiving layer and can be stripped with that layer from the photosensitive film. In the alternative, it may also provide the silver-receiving layer so that the positive print is formed in or on the surface thereof and the film obtained, upon drying of the processing agent, can either be stripped from this positive print or stripped with the positive print from the negative layer. In addition, the second sheet provides a protective covering over what would otherwise be an exposed surface of the liquid layer, thereby greatly minimizing oxidation when a dcveloper is used which is prone to aerial oxidation, and its presence keeps the liquid-spreading mechanism dry during the spreading. By using for this other sheet material an absorbent material, the removal of the liquid from the processing composition becomes more rapid and the provision of a solid film is accelerated.

In a preferred form of the process, the liquid composition is first located between the photosensitive silver halide element and another sheet material adjacent the area of the photosensitive element which is to be processed, and in sufiicient bulk to carry out the desired processing. The composition is thereafter spread in a thin layer over this area by squeezing it between the photosensitive element and the other sheet material. This is illustrated and described in detail in my Patent No. 2,647,056, issued July 28, 1953 for One Step Photographic Transfer Process.

The viscous liquid composition in its applied condition contains certain ingredients, some of which can be added to the composition during the spreading thereof but which are most simply introduced therein prior to the spreading. 'Ihese ingredients consist of:

(a) A silver halide developing agent;

(b) A substance for forming soluble silver complexes with silver halide, e. g., a silver halide solvent such as sodium thiosulfate;

() An organic heterocyclic compound from the class hereinabove identified for improving the effectiveness of the processing composition at elevated temperatures;

an (d) A thickening agent for increasing the viscosity of the composition.

Additionally, the composition may contain other ingredients, such for example as an alkali and sodium sulfite.

The relation of components employed in the performance of one form of the process of the present invention during a stage of said process is illustrated diagrammatically in Fig. 1 wherein: represents a photosensitive element comprising a support 10a and a photosensitive silver halide emulsion 10b; 12 represents a support or carrier layer for the transfer print which is obtained by the process; and 14 represents a layer of the relatively viscous liquid processing composition of the invention. Liquid layer 14 may be obtained by spreading the processing agent, for example in the manner disclosed in my Patent No. 2,647,056, between sheets 10 and 12.

The liquid composition may be provided for spreading as a layer 14 between elements 10 and 12 by being contained in an elongated rupturable container 16 which, as shown, has a length at least equal to the transverse dimension of the area of photosensitive element 10 to which it is to be applied. Container 16 may be attached to one of elements 10 and 12 and, as shown in Fig. 2, is suitably secured to the print-receiving surface of element 12. The container 16 is preferably inexpensive and disposable and so constructed as to be capable of retaining the liquid composition therein for relatively long periods of time without vapor loss or oxidation. One example of a suitable container of this type is formed from a single multilayer sheet of material comprising three laminae. The upper lamina, which provides the inner surface of the container, is formed of a material which is chemically inert to the processing agent and which is impervious to the liquid of the reagent. One class of materials suitable for this purpose, particularly where the processing composition is an alkaline solution, is the polyvinyl acetals, and of the acetals polyvinyl butyral is a preferred species. A composition comprising 60% to 72% by weight of polyvinyl butyral, 10% to 23% by weight of nitrocellulose, and approximately 5% by weight of dibutyl sebacate is satisfactory as the inner lamina. The intermediate lamina is preferably impervious to the vapor of the processing agent and is formed, for example, of a metallic foil such as lead or silver foil. The outer or backing lamina is formed of a strong, deformable, relatively inexpensive sheet material such as a kraft paper.

The container 16 is preferably formed by taking the single sheet of three-ply material and folding the same medially at 18, and thereafter securing the end marginal portions 20 and the longitudinal portions 22 of the two folded faces to one another, providing a central space or cavity 24 for containing the processing liquid.

To fill the container it is possible to adhere together the opposite longitudinally extending marginal portions 22 and one of the end marginal portions 20, the container being filled through the other end which is thereafter sealed.

Some of the ingredients contained in the processing composition after application thereof to the silver halide element may be added to the processing liquid as it is spread between elements 10 and 12, being so located on one or both of said elements as to be dissolved by, or otherwise interacted with, the liquid when the latter wets said element or elements.

Photosensitive element 10 is one of the commercially available photosensitive silver halide films, the term films being understood to include paper-backed emulsions. The present composition and process are particularly adapted to improve the results obtained when the higher speed photosensitive silver halide emulsions are used, such as the emulsion of the relatively high speed orthochromatic films, e. g., Eastman Kodak Verichrome Film, having an ASA speed rating of 0200 and an ASA exposure index rating in the daylight of 50, and the extremely high speed panchromatic emulsions, e. g., Eastman Kodak Super XX Pan having an ASA speed rating of 0400 and an ASA exposure index rating in the daylight of 100, and Ansco Triple S Pan.

Element 12, in the form shown, comprises a suitable support 12a which may be provided with a surface coating 12b, said coating carrying one or more of the reagents that are to be dissolved by the liquid composition as it is applied, and also preferably containing one or more stabilizing agents for improving the keeping quality of the transfer print. The stabilizing agents are materials which react subsequent to, or during the latter stages of, the silver precipitation to diminish the alkalinity of the layer 14 and are, for example, metallic salts or mixtures of salts which, in alkaline solution, consume alkalies by forming relatively insoluble metallic hydroxides with the hydroxyl ions of the alkali solution. The salts of such metals as zinc, cadmium, and lead give sufiiciently insoluble hydroxides to function satisfactorily as alkali-consuming agents. The acetates and nitrates of these metals are best. Also useful in this respect are organic compounds Which react in alkaline solution to absorb alkali such, for example, as dirnethyl oxalate, ethyl oxalate, dirnethyl tartrate and dimethyl malate.

The reagents in layer 1212 are preferably contained in a suitable vehicle which can be a film of polyvinyl alcohol, methyl cellulose, ethyl cellulose, sodium carboxymethyl cellulose, cellulose acetate-hydrogen phthalate, pectin, sodium alginate, gum arabic and other gums and resins, natural and synthetic, or a coating of micro-granular material as, for example, silica aerogel, kieselguhr or clay.

Examples of processes of the invention and examples of novel compositions and products useful in the performance of the processes are given below, but it is to be expressly understood that these examples are merely illustrative and that the invention is not necessarily limited to the specific materials, steps, or proportions set out therein.

The sodium carboxymethyl cellulose is dissolved first in the water in a mixer at room temperature. Thereafter, the sodium sulfite, sodium hydroxide, sodium thiosulfate, citric acid and chlorobenzotriazole are added to the solution, the addition being effected in an inert atmosphere of nitrogen. The hydroquinone is then added and the composition is mixed for an hour at approximately room temperature in a nitrogen atmosphere.

To 60 grams of the foregoing composition, there is then added 2 cc. of a fresh 1% sodium sulfide solution. After a thorough mixing there is added slowly, drop by drop, a solution comprising:

These additions produce a rich brown, highly dispersed, transparent suspension of sulfide salts.

The composition obtained in this way is then spread, as shown in Fig. 1, in a layer 14 of approximately .002-.0O3 in thickness between the baryta surface of a sheet of baryta paper 12 and the exposed photosensitlve silver halide emulsion b of a photosensitive film 10, said film 10, paper 12 and said composition being at a temperature of approximately 100 F. Emulsion 10b is a relatively high speed orthochromatic emulsion like the emulsion of Eastman Kodak Verichrome Film, and has a support 10a of a white paper. Elements 10 and 12 are kept superposed for approximately one minute and, at the end of this time, element 12 is stripped from element 10.

Element 12, when stripped, has on its surface a film of the solid residue of layer 14 and this film contains the precipitated silver so that the positive print is formed therein. Because of the absorption and evaporation of the liquid from layer 14, the film that is obtained is about one-tenth as thick as the original thickness of layer 14. The silver image in the film has good color and density, and because the transferred silver is precipitated so closely to the negative, the process gives an image of higher resolving power. Despite the elevated temperature at which the processing is performed, there is very little difference in density and tone from a print obtained at a temperature, for example, of 75 F. With very little loss in pictorial quality, a positive print can also be obtained by stripping the sheet 12 from the photosensitive element 10 less than fifteen seconds after the liquid is spread between elements 10 and 12.

Other materials may be substituted for those used in the foregoing process, and the proportions may be varied to an appreciable extent. For example, the film-forming material in the processing agent, which imparts the desired viscosity to the latter and maintains the silver reducing centers in suspension, may be any of the high molecular weight polymers which are stable to alkalies and which are soluble in aqueous alkaline solutions. For example, such other plastics as hydroxyethyl cellulose and the sodium salts of polymethacrylic acid and polyacrylic acid may be used. Preferably the plastic or other viscosity-imparting agent is contained in the composition in sufficient quantities to impart to the composition a viscosity in excess of 1000 centipoises at a temperature of approximately 24 C. The best results are obtained when the viscosities of the composition are of the order of 1000 to 400,000 ccntipoises at 24' C.

Where the processing composition is to be kept in storage for relatively long periods of time, it is desirable that the film-forming thickening agent in the composition be selected from materials which are relatively inert to alkalies and which, in an alkaline solution of a developmg agent, are not reduced by said developing agent and do not lose their viscosity-imparting characteristics. However, in the event the processing composition is to be used immediately or shortly after it is mixed, relatively hydrolyzable materials such as proteins, e. g., gelatin, and carbohydrates, e. g., the starches, can be employed as the film-forming thickening agents. The term film-forming colloid, as used herein, is understood to be generic to plastics, proteins and carbohydrates which, when dispersed in a liquid layer either in solution or suspension, will form a continuous solid film when the solvent is entirely removed as by evaporation and/ or absorption from the layer.

Although element 12 is preferably baryta paper, it or the outer layer thereof, which comes in contact with the developing composition, may be formed of such other materials as, for example, regenerated cellulose, polyvinyl alcohol, sodium alginate, cellulose ethers such as ethyl cellulose or their derivatives such as sodium carboxymethyl cellulose, aluminum carboxymethyl cellulose and hydroxyethyl cellulose, other papers, proteins such as gelatin, carbohydrates such as the starches, gum arabic, and other natural and synthetic resins as well as mixtures of these materials where the same are compatible.

Other developing agents may be used, for example one of the following: p-aminophenol hydrochloride; bromohydroquinone, chlorohydroqninone; diaminophenol hydrochloride; diaminophenol dihydrochloride; toluhydroquinone; monomethyl-p-aminophenol sulfate; and mix tures of monomethyl-p-aminophenol sulfate and hydroqumone.

To form a soluble silver complex such other silver halide solvents as potassium and ammonium thiosulfates and potassium, sodium and ammonium thiocyanates may be employed.

It is to be noted that in the composition of Example 1 certain silver-precipitating agents in the form of sulfide salts are provided in the processing composition as a result of which the precipitation of silver which gives the positive print is largely obtained in the film of processing agent. It is equally possible, and for many purposes more desirable, to provide these silver-precipitating agents on the surface of element 12, as, for example, by including the same in layer 1212, together with the stabilizing agents. The result of this arrangement is to concentrate the preparation of silver largely in the surface layer of element 12. When an element 12 so constructed is employed in the performance of the process, it may also be provided with a suitable overcoat of a material that diminishes the adhesion between the film formed by the processing agent and element 12 so that upon the separation of element 12 and photosensitive element 10, the film obtained by the relative drying of the processing agent adheres to said photosensitive element and is stripped from print-containing element 12.

Examples of suitable print-receiving elements 12 so constructed are set forth in the following two examples:

Example 2 A sheet of single-weight baryta paper is run through a bath containing 11 grams of cadmium acetate, .37 gram of lead acetate and 11 grams of zinc nitrate per 100 cc. of Water, preferably only one side of the sheet being in contact with the bath and this contact being for about 10 seconds. A mixture is then prepared by thoroughly mixing the following ingredients:

2700 cc. of water 278 grams of cadmium acetate 278 grams of zinc nitrate 93 grams of lead acetate 300 grams of silica aerogel 927 grams of a 3% water solution of sodium sulfide This mixture is then applied to the previously prepared baryta paper by running the paper through a bath of the mixture and removing excess by means of a soft rubber roll rotating counter to the direction of travel of the sheet.

Example 3 A sheet of single-weight baryta paper is run through a lead acetate and 18 grams of zinc nitrate per 100 cc. of

water,'preferably only one side of the sheet being in contact with the bath and this contact being for about 10 seconds. A mixture is then prepared by thoroughly mixing the following ingredients:

5400 cc. of water 55 6 grams of cadmium acetate 1112 grams of zinc nitrate 186 grams of lead acetate 600 grams of silica aerogel 1894 grams of a 3 water solution of sodium sulfide This mixture is then applied to the previously prepared baryta paper by running the paper through a bath of the mixture and removing excess by means of a soft rubber roll rotating counter to the direction of travel of the sheet.

When the print-receiving elements 12 formed in accordance with either of the foregoing examples and provided with no further surface treatment are used in the transfer processes, the silver for forming the positive print is precipitated predominantly in layer 12b and the film formed by the processing agent, in general, adheres to the print-receiving element when said element is stripped from photosensitive element 10. However, by providing a suitable stripping coating on the surface of element 12, it becomes possible to diminish the adhesion between the film formed by the processing agent and element 12 to the extent that upon the separation of element 12 and element 10 said film will adhere to element 10.

To provide an element 12 having a suitable stripping overcoat, the elements of either of Examples 2 or 3 may' be suitably further processed in the following manner:

Example 4 The processed sheet of Examples 2 or 3 has roll-coated thereon against a smooth surface such, for example, as the polished surface of a metal drum, a 5% aqueous'solution of polyvinyl alcohol in a layer whose thickness is of the order of .001 inch. In a similar manner, such other materials as methyl cellulose, sodium alginate, ethyl cellulose, gum arabic and pectin may be applied as a stripping overcoat to element 12.

When the print-receiving elements 12 are formed, as set out in the foregoing examples, in the performance of the process the silver-precipitating agents, i. e., the sulfide salts, may be omitted from the processing agent, the latter comprising the following constituents:

Example 5 1860 cc. of water 107 grams of medium viscosity sodium carboxymethyl cellulose 12i1 grams high viscosity sodium carboxymethyl celluose 78.0 grams of sodium sulfite 74.6 grams of sodium hydroxide 14.5 grams of sodium thiosulfate 38.5 grams of citric acid 52.0 grams of hydroquinone 1.5 grams of chlorobenzotriazole In lieu of the chlorobenzotriazole of Examples 1 and 5, there may be substituted one or a mixture of two or more of the following ingredients: 6-nitrobenzimidazole, benzotriazole, S-nitrobenzotriazole, S-methyl benzimidazole. These compounds may be made constituents of the composition by being added thereto in the form of their soluble salts. For example, 6-nitrobenzimidazole may be dissolved into the composition in the form of G-nitrobenzimidazole nitrate. Instead of being contained in the composition prior to the application of the composition to the photosensitive element, these compounds may also be introduced into the composition for the first time after the composition is spread by being contained for example in layer 12b of element 12. It is, however, very much preferable to incorporate these compounds in the composition prior to its application to the photosensitive element.

The novel class of materials of the present invention is to be distinguished from materials such as potassium bromide which render the processing composition operative at elevated temperatures but which have the effect of retarding the diffusion of the silver into the positive when the processing is performed at more normal ambient temperatures such as 70 C.

To illustrate the eflicacy of the select group of com- 1 pounds of the present invention for improving the quality of the transfer prints obtained at elevated temperatures there follows a table of comparative data obtained by using these addition agents and other agents which have been suggested for anti-fogging purposes. These materials were used in the same silver halide diffusion transfer reversal process, the photosensitive element, the print-receiving element, and, except for the listed addition agent, the processing composition being exactly the same in each case. The same subject matter was photographed under the same conditions and the maximum density of the resulting positive print was measured when the process was performed at a room temperature of approximately 70 F. and when it was performed at an elevated temperature of approximately 110 F.

D Max. D Max. Compound ggfi Room 1 hr.

Temp. 110 F.

Control-nothing arid ed 1. 48 1. 02 1:800 1. 63 1. 68 Chlorobenzotrlazole" 1:600 1. 56 1. 64 ea :2: 6-mtrobenz1midazole 2g 1:1600 1. 51 1. 48 1:800 1. 55 1. 61 fi-methyl benzimidazole 1: 1600 1. 63 1. 60 1:31:00 1. 66 1. e2 5-n1trobenzotriaml 1:600 1. 69 1. 61 1:100 1. 52 1. 63 1:600 1. 67 1. 33 Sulfathla 1:50 1. 47 1. 28 1:40 1. 51 1. O0 1:000 1.65 131 Ammotetrazole 1: 50 1. 59 1. 22 1:40 1. 50 1. 12 1:600 1. 60 1. 28 2-1nethyl benzothlazole 1:50 1. 52 0. 59 1:40 1. 52 0. 59 1:600 1. 04 1. 24 dl-histidme hydrochloride 1:50 1. 60 0. 58 1:40 1. 60 0. 58 1:600 1. 50 0. 70 o-chloroanlhne 1:50 1. 56 0. 64 1:40 1. 5s 0. s4

m-chloroamlme 1:000 1. 40 0. DL-mandehc acid 1:50 1. 58 0. 76 1:40 1. 55 0. 70

l Same as o-chloroaniline.

ment, a silver halide developed for developing the latent 1 image in said layer, a silver halide solvent for forming soluble silver complex with the undeveloped silver halide of said layer and a substance for rendering said composition effective at elevated temperatures, said last-named substance being a compound having the following formula:

wherein X is attached to one of the unshared carbon atoms of the benzene ring and is one of H,NOz,Cl and CH3 and wherein Y is one of CH and N, causing the silver halide developer to develop the latent image and the silver halide solvent to form with the undeveloped silver halide a soluble silver complex, transferring said silver complex by diffusion to a print-receiving material,

and causing the silver of said complex to be reduced in said material to form therein a positive print of the subject matter of said latent image.

2. The process of claim 1 wherein said compound is chlorobenzotriazole.

3. The process of claim 1 6-nitrobenzimidazole.

4. The process of claim 1 benzotriazole.

5. The process of claim 1 S-methyl benzimidazole.

6. The process of claim 1 S-nitrobenzotriazole.

7. A photographic process for forming by transfer a positive print of a latent image contained in a silver halide layer of a photosensitive element which comprises the steps of applying to said element a processing composition comprising a silver halide developer for developing the latent image in said layer, a silver halide solvent for forming soluble silver complex with the undeveloped silver halide of said layer and a substance rendering said composition effective at elevated temperatures, said lastnamed substance being a compound having the following formula:

N g X Y wherein X is attached to one of the unshared carbon atoms of the benzene ring and is one of H, N02, Cl and C and wherein Y is one of CH and N, causing the silver halide developer to develop the latent image and the silver halide solvent to form with the undeveloped silver halide a soluble silver complex, transferring said silver complex by diffusion to a print-receiving material, and causing the silver of said complex to be reduced in said material to form therein a positive print of the subject matter of said latent image.

8. The process of claim 7 wherein said compound is chlorobenzotriazole.

9. The process of claim 7 wherein said compound is 6-nitrobenzimidazo1e.

10. The process of claim 7 wherein said compound is benzotriazole.

11. The process of claim 7 wherein said compound is S-methyl benzimidazole.

12. The process of claim 7 wherein said compound is S-nitrobenzotriazole.

13. A photographic process for forming by transfer a wherein said compound is wherein said compound is wherein said compound is wherein said compound is positive print of a latent image contained in the silver halide emulsion of a photosensitive element which comprises the steps of applying between said photosensitive element and a print-receiving element a relatively thin, uniform layer of a thickened liquid composition comprising a silver halide developer for developing the latent image in said layer, a silver halide solvent for forming soluble silver complex with the undeveloped silver halide of said layer and a substance for rendering said composition eifective at elevated temperatures, said last-named sublstance being a compound having the following formu a:

wherein X is attached to one of the unshared carbon atoms of the benzene ring and is one of H, N02, Cl and CH3 and wherein Y is one of CH and N, causing the silver halide developer to develop the latent image and the silver halide solvent to form with the undeveloped silver halide a soluble silver complex, transferring said silver complex by diffusion to said print-receiving element and causing the silver of said complex to be reduced in said print-receiving element to form therein a positive print of the subject matter of said latent image.

14. The process of claim 13 wherein said compound is chlorobenzotriazole.

15. The process of claim 13 wherein said compound is 6-nitrobenzimidazole.

16. The process of claim 13 wherein said compound is benzotriazole.

17. The process of claim 13 wherein said compound is S-methyl benzimidazole.

18. The process of claim 13 wherein said compound is S-nitrobenzotriazole.

References Cited in the file of this patent UNITED STATES PATENTS 2,324,123 Weissberger July 13, 1943 2,384,593 Bean Sept. 11, 1945 FOREIGN PATENTS 59,365 Netherlands Apr. 17, 1947 

1. A PHOTOGRAPHIC PROCESS FOR FORMING BY TRANSFER A POSITIVE PRINT OF A LATENT IMAGE CONTAINED IN A SILVER HALIDE LAYER OF A PHOTOSENSITIVE ELEMENT WHICH COMPRISES THE STEPS OF APPLYING TO SAID ELEMENT A PROCESSING COMPOSITION WHICH COMPRISES, UPON APPLICATION TO SAID ELEMENT, A SILVER HALIDE DEVELOPED FOR DEVELOPING THE LATENT IMAGE IN SAID LAYER, A SILVER HALIDE SOLVENT FOR FORMING SOLUBLE SILVER COMPLEX WITH THE UNDEVELOPED SILVER HALIDE OF SAID LAYER AND A SUBSTANCE FOR RENDERING SAID COMPOSITION EFFECTIVE AT ELEVATED TEMPERATURES, SAID LAST-NAMED SUBSTANCE BEING A COMPOUND HAVING THE FOLLOWING FORMULA: 